So for my 10 gallon tank I just had cabomba in it before which did really well with the riverstones I have in there. The gravel is a bit larger than the average stuff, so when I planted my java fern and a little bunchy plant with lots of roots (I bought it last night and completely forgot what it was called), they're having a hard time staying under this gravel. What I was thinking of doing was buying a finer subtrate like sand or something to plant them in and then put the gravel on top of the new substrate. Will this work? What kind of substrate should I use? Is there a chance I can just use potting soil or something?

It is difficult to get rooted plants to stay planted until they get more roots. I have pea gravel in almost all of my tanks, I bury the roots & push the gravel as tight as I can & some pants will still float to the top for a while.